The invention relates to tripod joints. The joints include an outer joint part, with three circumferentially distributed longitudinal recesses each forming circumferentially opposed tracks, and an inner Joint part, with tripod arms which extend into the longitudinal recess and support rolling members movably and pivotably held on the tripod arms in rolling contact with the tracks. The longitudinal recesses are provided with guiding means to hold the rolling members in the longitudinal recesses so as to be axis-parallel with the inner joint part.
Examples of tripod joints are DE 39 36 601, DE 28 31 044 or DE 37 16 962 C 2. Although these designs solve the problem of a free rolling movement of the rolling members in the tracks under rotation and articulation conditions, the shape of the rolling members during the radially inwardly directed movement of the arms may cause the rolling members to jam between the shoulders at the longitudinal recesses which prevent the rolling members from rolling freely. Attempts have been made to provide intermediate members not participating in the rolling movement. An example of intermediate members are collars arranged at the roller carrier, which collars accommodate the radial forces, thereby preventing the rollers from jamming. As a result, the roller assembly needs to consist of a plurality of parts and becomes expensive. Functional advantages are achieved at considerable additional costs.
It is the object of the present invention to provide a tripod joint which eliminates roller jamming in the tracks caused by the radial movement component of the arms relative to the rollers when the joint rotates in an articulated condition.
The objective is achieved by providing a first contact point for accommodating a circumferentially extending transmission force in the region of a central roller plane and at least one second contact point for accommodating an inwardly directed guiding force in the region of a radially inner supporting shoulder. The central plane of the roller is the plane containing the first contact point relative to the track when the joint is in an extended condition and extending perpendicularly relative to the arm axis. In most cases, the plane is also the geometric axis of symmetry and height-bisecting plane of the roller region coming into contact with the track.
In accordance with the objective of the invention, this measure ensures that the first contact point for torque transmission is substantially constant from the point of view of position and direction. The transmission forces do not influence the radial guiding forces for the rollers, which are accommodated in a second contact point. A tangential plane on the surfaces of the first contact point extends either parallel to the arm axis or it opens outwardly at an angle relative to the arm axis, with an outwardly directed reaction force acting at the first contact point on the roller becoming effective in the latter case. The constancy of the position of the contact point is ensured by large curved surfaces of the track and/or the rolling member. The large-area curvature of the surface includes an infinite radius of curvature. In the region of the first contact point the rolling member may be cylindrical or spherical and the track surface may be planar, with the counter-face in the cross-section through the joint comprising a curvature with a large radius. It is also possible for both surfaces in the cross-section through the joint to be curved. However, it is preferable, in each case, to select radii of curvature which are clearly greater than the greatest rolling radius of the rolling member itself. The second contact point accommodating the guiding forces is positioned radially inside the first contact point, with the tangential plane on the surface in this contact point in the region of the guiding shoulders inclined by approximately 45.degree. relative to the arm axis. A third contact point symmetrical relative to the first contact point may be provided radially outside, at a further guiding shoulder of the track. It is proposed that the roller should be able to move with radial play between the first and third contact points. The functioning of the third contact point may also be ensured by simple contact of the rolling member or parts related thereto with the base of the longitudinal recess itself.
The subject of the invention is generally applicable to joints in which the head of the arm element slides pivotably and radially movably in an internally cylindrical roller and bearing carrier; to joints with a two-part roller and bearing carrier comprising inner and outer rings pivotable relative to each other, the inner ring being radially movable on a cylindrical arm; and to joints which the internally cylindrical face of the rolling member slides on an externally spherical face of an inner ring so as to be pivotable and radially movable, the inner ring being rotatably supported on a cylindrical arm.
From the following detailed description taken in conjunction with the accompanying drawings and subjoined claims, other objects and advantages of the present invention will become apparent to those skilled in the art.